Surveys have indicated that a significant percentage of water obtained from individual taps in the home contains one or more bacterialogical or chemical constituents that exceed limits set forth in standards issued by public health services. The problem may be more acute in rural areas where water used for drinking and cooking is taken from natural sources and is used without any treatment. In some cases, such samples evidence a potential danger to public health, and in other cases adversely affect the potability of the water.
A multitude of contaminants have also been identified in various drinking water supplies in the United States. In particular, according to a recent report on water detoxification, more than 700 specific organic chemicals have been isolated from U.S. water supplies. These contaminants result for such diverse sources as industrial and municipal discharges, urban and rural runoff, and natural decomposition of vegetative and animal matter, as well as from water and sewage chlorination practices. Concentrations of contaminants vary from virtually nil in protected ground water to substantial levels in many surface waters and contaminated ground waters.
Organic chemical contaminants in drinking water can be divided into two major classes: those of natural origin and those of synthetic origin. The natural substances represent by far the greatest portion and consist primarily of undefined humus and fulvic materials and other substances produced by normal organic decomposition or biotic transformation and, in general, are not known to be harmful in themselves. These natural substances do, however, give rise to the undesirable odor and color which render drinking water non-potable or distasteful.
The synthetic chemicals in water can be subdivided into two groups. The first group consists of those chemicals that result from water treatment practices (e.g., chlorine and chloramine treatment), which treatment gives rise to trihalomethanes. Recent EPA studies indicate that, except for certain cases, trihalomethanes constitute the largest portion of the identifiable synthetic chemicals present in drinking water. Unlike other synthetic chemicals present in water supplies, chloroform and other trihalomethanes are formed during the treatment process. They are thus found in virtually every drinking water supply that is disinfected with chlorine, and not uncommonly at concentrations of several hundred parts per billion. Other studies indicate that trihalomethanes may represent only a portion of the total halogenated products resulting from chlorination of water. Halogenated organics such as carbon tetrachloride, and hexachloroethane have also been detected in parts per million levels as contaminants in chlorine supplies used in various water treatment processes.
When the water treatment occurs in a permenantly installed water treatment system, prolonged storage, mechanical filtration and sedimentation may reduce the concentration of contaminants. However, the problem of contaminant removal is severe in temporary or portable treatment systems which are used at remote construction sites and by the armed forces on field maneuvers.
The second group of synthetic chemicals consists of those chemicals introduced into water supplies as a result of point and non-point sources of pollution. Nationally, both surface waters and to a lesser degree ground waters are contaminated with a variety of these pollution-related synthetic organic chemicals ranging from the low molecular weight halogenated hydrocarbons and monocyclic aromatic compounds to higher molecular weight pesticides, polycyclic aromatic compounds, and pesticide-like compounds.
The chemicals thus far identified in drinking water account for only a small fraction of the total organic content. Hence, the possibility, and indeed the probability, exists that additional substances of equal or greater toxicological significance may be present in water supplies.
The problem of contaminated water supplies has stimulated an abundance of research and development for treatment techniques for controlling the levels of contaminants in drinking water as well as for removing undesirable and aesthetically displeasing odor, and color therefrom. Public awareness of the problem has spawned several solutions of varying effectiveness.
One answer has been a steadily increasing usage of sterilized water or bottled water. At the same time, there have been a number of entries into the marketplace of point-of-use purification devices. The latter have included in-line filters, under-the-sink filters, free-standing drink-size separate filter units and filter devices that attach to the conventional sink faucet or to the typical aerator secured thereto.
In general, a somewhat limited number of processes have been found to be capable of removing undesired materials from water. These include reverse osmosis, freezing, filtration, chemical oxidation, distillation, adsorption on powdered charcoal and adsorption on granular activated carbon. Carbon filtration has been found to be particularly effective in removing some detergents, insecticides, viruses, specific chemical pollutants and taste and odor pollutants. For example, carbon has long been used for the removal of chlorine from water in the brewing and soft drink manufacturing industries. Activated carbon removes tastes and odors from water by an adsorption process in which substances of one kind are accumulated on the surfaces of another. The activated carbon has extremely large surface areas that make it efficient. The activation process produces pores that contribute substantially to increased surface area of treatment. In some cases, the activated carbon has been treated with oligodynamic silver which acts as a bactericide and self-sanitizing agent.
Filtered water for drinking or cooking is available in bottles and other containers, but for effective filtration with conventional equipment, it is necessary to provide mechanical filters which generate a sufficient head or pressure differential across the filter medium to assure an economic rate of flow through the filter medium. Such equipment is expensive and space-consuming and operation thereof for an entire water system is not practical.
It is evident that a continuing need exists for improved systems to control the levels of contaminants present in drinking water, both harmful contaminants such as trihalomethanes and aesthetically undesirable constituents which render the water non-potable.